1. Field of the Invention
This invention relates to polysulfide polymer latex based sealant and caulking compositions. More particularly, this invention relates to polysulfide polymer latex-urethane prepolymer sealant compositions having significantly improved physical properties.
2. Description of the Prior Art
Polymer latex based caulking compositions are known in the art. They are economically attractive sealant compositions characterized by their excellent application characteristics; i.e., they are readily gunned, troweled, or beaded onto various surfaces. These latex caulks have been extensively used for a variety of coating, caulking, and grouting applications, e.g. sealing panes of glass to window frames, sealing cracks in concrete structures, sealing basedboard and trim seams, sealing around bath tubs, sealing boat hulls, etc. Latex based caulking compositions of the prior art have in general been based upon solvent or water dispersions of such polymers as the polyacrylates, polyvinyl acetates, polysulfides and the like. In addition to the polymer latex, these prior art latex based caulking compositions frequently contained special purpose additives such as fillers, plasticizers, adhesive additives, latex stabilizers, and the like. As is known to those skilled in the art, latex caulks of the above type do not cure in the standard sense. That is, they do not cure through the use of oxidative curing agents or crosslinkers but rather attain their maximum physical properties through solvent or water evaporation and subsequent coalescing of the dispersed polymer particles.
While the latex caulks referred to above have proven useful in certain applications, they all have been found to possess several serious shortcomings. Thus, the prior art latex caulks exhibited relatively low physical properties, moderate to high shrinkage, poor underwater adhesion, poor resistance to rain washout and high cost. In addition to the foregoing disadvantages prior art polysulfide latex caulks often exhibited objectionable odors.
In addition to the latex caulks, 100% solids moisture and air curable sealants are also in common usage. Two common types are polysulfide and polyurethane based. These sealants have little or no shrinkage, high physical properties, and good resistance to washout prior to ultimate cure. However, they have the disadvantages of slow cure, long "paint-over" times, poor sag resistance, poor blading properties, difficult clean-up problems, poor one-package stability, difficult production problems, erratic adhesion values, and high cost. 100% Solids moisture curable sealants based on blends of urethane prepolymers with SH terminated liquid polysulfide polymers are also known in the art. Thus, U.S. Pat. No. 2,929,794 describes a sealant composition comprising from 5-95% by weight of an amine curable urethane prepolymer and from 95-5% by weight of an SH terminated liquid polysulfide polymer, co-cured with a mixture of an amine catalyst for the urethane and a peroxide catalyst for the SH terminated liquid polysulfide polymer.
The sealant compositions of the present invention are readily distinguishable from the compositions of U.S. Pat. No. 2,929,794. Thus, the product of the reaction of the urethane prepolymer with the SH terminated liquid polysulfide polymers described in the patent must produce a block copolymer. This necessarily occurs since the NCO terminals of the urethane prepolymer will react with the SH terminals of the liquid polysulfide polymers to produce a copolymer containing alternating block or segments of each polymer. On the other hand, the compositions of the present invention employ a polysulfide polymer latex of a high molecular weight polysulfide polymer which does not have SH terminals as indicated in the description of the polysulfide polymer latex which follows. Accordingly, the product of the urethane prepolymer and polysulfide polymer latex of the present compositions is a mixture of fully chain extended polymers rather than a block copolymer as necessarily results from the patented compositions. Moreover, the compositions of the present invention are further distinguishable from the compositions of the above mentioned patent in that no separate curing agents are required for the polysulfide polymer latex or the urethane prepolymer. This is true since the polysulfide polymer latex requires no oxidative curing agent as it does not contain SH terminals, but cures merely through a coalescing of polymer particles on evaporation of water from the latex while the urethane prepolymer cures by utilizing the water from the polysulfide polymer latex.
Moreover, the urethane prepolymer-SH terminated liquid polysulfide polymer blends described in U.S. Pat. No. 2,929,794 exhibit the same disadvantages as the 100% solid moisture curable polysulfide or polyurethane based sealants referred to previously, e.g., slow cure, long paint-over times, poor blading properties, poor physical properties, etc.
The polysulfide latex-urethane prepolymer blends of the present invention achieves virtually all of the advantages of the prior art latex caulks (including prior polysulfide latex caulks) and the 100% solids moisture curable one-package sealants but without most of their disadvantages. Thus, the polysulfide latex-urethane prepolymer blend compositions of the present invention is an economically attractive sealant having improved tensile, elongation, adhesion, and sag resistance as well as relatively rapid drying times, short paint-over times, and excellent application characteristics. Moreover, the polysulfide latex-urethane prepolymer blends of the present invention can be readily cleaned up with water. This last feature is especially attractive in confined areas where solvent odors are objectionable. Finally, the sealant composition of the present invention is relatively odor free.
Accordingly, it is an object of the present invention to produce a polysulfide latex based sealant and caulking composition having improved physical properties. More particularly, it is an object of the present invention to produce a polysulfide latex based sealant and caulking composition having improved tensile, elongation, adhesion, sag resistance, resistance to rain washout, and application characteristics. It is a still further object of the invention to produce a sealant and caulking composition which is readily cleaned up with water and is relatively odor free. Further objects of the invention will be readily apparent to those skilled in the art from the detailed description which follows.